Resolve all 33 medium-severity architecture review findings

Second slice of the 2026-09-09 whole-system review remediation
(docs/plans/2026-09-09-arch-review.md §10), on top of the High slice 146a1323.

Runtime/devices: SR-2 alarm on-trigger integration scope; SR-3 correlated NativeAlarmActor
subscribe retry; SR-4 immutable audited DB target; SR-5 ordered InstanceActor stop/flush;
SR-12 rehydration fence; SR-13 S&F gate recheck per delivery; DC-4 no OPC UA security
downgrade; DC-5 alarm snapshot for every new subscriber; ORCH-1 sync-dispose joins the pump.

Management/UI: MG-2 site scope on audit tree + Flow Debugger Replay; MG-3 stale-probe memo
removed; MG-4 server-owned bulk-deploy deadline; UI-5 sandbox runs in a killable child
process (new CentralUI.SandboxWorker project); UI-14 bounded sandbox output/IPC.

Edge/audit: EI-1 relay audit ownership; EI-2 SkipBodyCapture suppresses error text; EI-3/EI-11
error-field redaction + caps; EI-4 single relay deadline, pre-execution-only retry; EI-5
authenticated relay provenance; EI-10 body cap before audit read.

Persistence/contracts: DL-1 global Instance.UniqueName unique index + conflict translation;
DL-2 DataConnection protocol config encrypted at rest (migration
20260909203046_EnforceGlobalInstanceNamesAndProtectProtocolConfiguration — coordinated
central upgrade, old binaries cannot read protected rows); DL-3 bounded Replay paging;
DL-6 cross-site Overwrite of a deployed instance rejected; XC-4 proto descriptor contract test.

Config/hygiene: XC-1 central listener isolation by local port; XC-2/XC-3 inert SMTP + cron
keys removed from rig settings; CM-2 env2 bootstrap guard enabled; DC-6 deploy site exit code;
DC-7 notifier retries only explicit standby rejection; XC-5 ClusterClient purged from docs.

Gates recorded in the report: build 0/0, 9 397 passed / 0 failed, rig redeployed on all
eight nodes with the migration applied. 46 Low findings remain open.

tests/ZB.MOM.WW.ScadaBridge.DeploymentManager.Tests/DeploySiteAsyncTests.cs

@@ -299,15 +299,19 @@ public class DeploySiteAsyncTests : TestKit
                     new FlatteningPipelineResult(config, "sha256:3", ValidationResult.Success()));
             });
 
+        var tracker = new ConcurrencyTracker();
         var commActor = Sys.ActorOf(Props.Create(() =>
-            new ThrottledSiteActor(new ConcurrencyTracker(), slowInstanceName: null, slowDelay: TimeSpan.Zero)));
+            new ThrottledSiteActor(tracker, slowInstanceName: null, slowDelay: TimeSpan.Zero)));
 
         var service = CreateService(commActor, maxParallelism: 2);
 
-        await Assert.ThrowsAnyAsync<OperationCanceledException>(
-            () => service.DeploySiteAsync(SiteId, "admin", cancellationToken: cts.Token));
+        var result = await service.DeploySiteAsync(SiteId, "admin", cancellationToken: cts.Token);
+        Assert.True(result.IsSuccess);
+        Assert.Equal(6, result.Value.FailureCount);
+        Assert.Equal(0, result.Value.SuccessCount);
 
         Assert.Equal(0, _lockManager.TrackedLockCount);
+        Assert.Equal(0, tracker.MaxObserved); // No command may dispatch after the preparation deadline.
 
         // No prepared deployment may be left InProgress.
         await _repo.Received().UpdateDeploymentRecordAsync(

tests/ZB.MOM.WW.ScadaBridge.DeploymentManager.Tests/StaleInstanceProbeTests.cs

@@ -52,7 +52,18 @@ public class StaleInstanceProbeTests
     private StaleInstanceProbe CreateProbe() => new(_pipeline, _watermark);
 
     [Fact]
-    public async Task UnchangedWatermark_ServesMemoisedHash_WithoutReflattening()
+    public async Task PeerEdit_WithIndependentWatermark_IsObservedByWarmActiveProbe()
+    {
+        var active = CreateProbe();
+        var peer = new TemplateGraphWatermark();
+        Assert.Equal("sha256:first", await active.GetCurrentRevisionHashAsync(InstanceId));
+        _currentHash = "sha256:peer-edit"; // Shared database changed through another central.
+        peer.BumpAll();
+        Assert.Equal("sha256:peer-edit", await active.GetCurrentRevisionHashAsync(InstanceId));
+    }
+
+    [Fact]
+    public async Task UnchangedWatermark_StillReflattensAuthoritatively()
     {
         var probe = CreateProbe();
 
@@ -60,7 +71,7 @@ public class StaleInstanceProbeTests
         Assert.Equal(1, _flattenCount);
 
         Assert.Equal("sha256:first", await probe.GetCurrentRevisionHashAsync(InstanceId));
-        Assert.Equal(1, _flattenCount);
+        Assert.Equal(2, _flattenCount);
     }
 
     /// <summary>
@@ -77,13 +88,13 @@ public class StaleInstanceProbeTests
         // The underlying config drifted (e.g. a data connection was repointed).
         _currentHash = "sha256:second";
 
-        // Without a bump the stale hash would still be served...
-        Assert.Equal("sha256:first", await probe.GetCurrentRevisionHashAsync(InstanceId));
+        // Even without a local bump, a peer edit is authoritative.
+        Assert.Equal("sha256:second", await probe.GetCurrentRevisionHashAsync(InstanceId));
 
         _watermark.BumpAll();
 
         Assert.Equal("sha256:second", await probe.GetCurrentRevisionHashAsync(InstanceId));
-        Assert.Equal(2, _flattenCount);
+        Assert.Equal(3, _flattenCount);
     }
 
     [Fact]